/*
 * Copyright 2002-2007 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.core.io;

import org.springframework.util.ResourceUtils;

/**
 * #Comment#:能够根据资源的地址，判断资源的类型,并返回对应的Resource实现类。因为所有的应用上下文需要加载资源，
 * 所以ApplicationContext扩展了这个接口。
 * <p/>
 * 加载资源(例如class path或者文件系统的资源)的策略接口。
 * {@link org.springframework.context.ApplicationContext}需要提供这个功能，并扩展
 * {@link org.springframework.core.io.support.ResourcePatternResolver} 的支持。<br/>
 * Strategy interface for loading resources (e.. class path or file system
 * resources). An {@link org.springframework.context.ApplicationContext} is
 * required to provide this functionality, plus extended
 * {@link org.springframework.core.io.support.ResourcePatternResolver} support.
 * 
 * <p>
 * {@link DefaultResourceLoader} is a standalone implementation that is usable
 * outside an ApplicationContext, also used by {@link ResourceEditor}.
 * 
 * <p>
 * Bean properties of type Resource and Resource array can be populated from
 * Strings when running in an ApplicationContext, using the particular context's
 * resource loading strategy.
 * 
 * @author Juergen Hoeller
 * @since 10.03.2004
 * @see Resource
 * @see org.springframework.core.io.support.ResourcePatternResolver
 * @see org.springframework.context.ApplicationContext
 * @see org.springframework.context.ResourceLoaderAware
 */
public interface ResourceLoader {

	/** Pseudo URL prefix for loading from the class path: "classpath:" */
	String CLASSPATH_URL_PREFIX = ResourceUtils.CLASSPATH_URL_PREFIX;

	/**
	 * Return a Resource handle for the specified resource. The handle should
	 * always be a reusable resource descriptor, allowing for multiple
	 * {@link Resource#getInputStream()} calls.
	 * <p>
	 * <ul>
	 * <li>Must support fully qualified URLs, e.g. "file:C:/test.dat".
	 * <li>Must support classpath pseudo-URLs, e.g. "classpath:test.dat".
	 * <li>Should support relative file paths, e.g. "WEB-INF/test.dat". (This
	 * will be implementation-specific, typically provided by an
	 * ApplicationContext implementation.)
	 * </ul>
	 * <p>
	 * Note that a Resource handle does not imply an existing resource; you need
	 * to invoke {@link Resource#exists} to check for existence.
	 * 
	 * @param location
	 *            the resource location
	 * @return a corresponding Resource handle
	 * @see #CLASSPATH_URL_PREFIX
	 * @see org.springframework.core.io.Resource#exists
	 * @see org.springframework.core.io.Resource#getInputStream
	 */
	Resource getResource(String location);

	/**
	 * Expose the ClassLoader used by this ResourceLoader.
	 * <p>
	 * Clients which need to access the ClassLoader directly can do so in a
	 * uniform manner with the ResourceLoader, rather than relying on the thread
	 * context ClassLoader.
	 * 
	 * @return the ClassLoader (never <code>null</code>)
	 */
	ClassLoader getClassLoader();

}
